What is Nuclear fission: Definition and 88 Discussions

Nuclear fission is a reaction in which the nucleus of an atom splits into two or more smaller nuclei. The fission process often produces gamma photons, and releases a very large amount of energy even by the energetic standards of radioactive decay.
Nuclear fission of heavy elements was discovered on December 17, 1938 by German Otto Hahn and his assistant Fritz Strassmann at the suggestion of Austrian-Swedish physicist Lise Meitner who explained it theoretically in January 1939 along with her nephew Otto Robert Frisch. Frisch named the process by analogy with biological fission of living cells. For heavy nuclides, it is an exothermic reaction which can release large amounts of energy both as electromagnetic radiation and as kinetic energy of the fragments (heating the bulk material where fission takes place). Like nuclear fusion, in order for fission to produce energy, the total binding energy of the resulting elements must be greater than that of the starting element.
Fission is a form of nuclear transmutation because the resulting fragments (or daughter atoms) are not the same element as the original parent atom. The two (or more) nuclei produced are most often of comparable but slightly different sizes, typically with a mass ratio of products of about 3 to 2, for common fissile isotopes. Most fissions are binary fissions (producing two charged fragments), but occasionally (2 to 4 times per 1000 events), three positively charged fragments are produced, in a ternary fission. The smallest of these fragments in ternary processes ranges in size from a proton to an argon nucleus.
Apart from fission induced by a neutron, harnessed and exploited by humans, a natural form of spontaneous radioactive decay (not requiring a neutron) is also referred to as fission, and occurs especially in very high-mass-number isotopes. Spontaneous fission was discovered in 1940 by Flyorov, Petrzhak, and Kurchatov in Moscow, in an experiment intended to confirm that, without bombardment by neutrons, the fission rate of uranium was negligible, as predicted by Niels Bohr; it was not negligible.The unpredictable composition of the products (which vary in a broad probabilistic and somewhat chaotic manner) distinguishes fission from purely quantum tunneling processes such as proton emission, alpha decay, and cluster decay, which give the same products each time. Nuclear fission produces energy for nuclear power and drives the explosion of nuclear weapons. Both uses are possible because certain substances called nuclear fuels undergo fission when struck by fission neutrons, and in turn emit neutrons when they break apart. This makes a self-sustaining nuclear chain reaction possible, releasing energy at a controlled rate in a nuclear reactor or at a very rapid, uncontrolled rate in a nuclear weapon.
The amount of free energy contained in nuclear fuel is millions of times the amount of free energy contained in a similar mass of chemical fuel such as gasoline, making nuclear fission a very dense source of energy. The products of nuclear fission, however, are on average far more radioactive than the heavy elements which are normally fissioned as fuel, and remain so for significant amounts of time, giving rise to a nuclear waste problem. Concerns over nuclear waste accumulation and the destructive potential of nuclear weapons are a counterbalance to the peaceful desire to use fission as an energy source.

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  1. A

    I Why Does Gravity Remain when Star Mass Dissipates?

    Stars have mass. This mass has a gravitational pull. The nuclear fission of the star pushes against the effects of gravity. Why doesn't the gravity reduce as the star burns more and more of the hydrogen/helium/carbon that it's made up of? In other words, how can a black hole be created when the...
  2. humanlearning369

    35 years in technology as programmer/engineer

    I'm working on a Python-based project to simulate fission energy containment. Details and GitHub link for collaboration coming soon. Looking forward to contributions.
  3. D

    Have pulsed fission reactors got any potential in nuclear energy?

    How did you find PF?: Searched for some forum about mechanical engineering in Google Do pulsed nuclear fission reactors have any chances to be used in nuclear power? If the answer is "no" is that just because of no need in pulsed operation mode while having a common one, are there any more...
  4. resurgance2001

    Nuclear Fission Energy and Mass Loss

    (112 x 8.36 + 122 x 8.51) - 235 x 7.59 = 190.89 MeV My question is what should I do about the incoming neutron on the left that starts the fission. My thinking is that it does not have any binding energy and therefore I left it out of the calculation. Is that correct? Thank you
  5. NewPhysi

    I Nuclear Fission of Uranium-235

    I'm learning about nuclear fission for fun, well based on my research, 82% of the time that uranium-235 absorbs a neutron it will fission, the uranium-235 will briefly turn into an excited uranium-236 and after that, it will split, the other 18% of the time it will just emit radiation and...
  6. Leo Liu

    Binding energy and nuclear fission

    If I am not mistaken, binding energy is the energy required to separate the constituents of the nucleus, and is always a positive number. However, if splitting elementary particles in the nucleus apart requires energy, then why do fission reactions release energy?
  7. M

    Other Creating a Nuclear Fission Reactor

    How do I create a nuclear fission reactor? if you can link me up to any places to buy the things or any other sites that would be good.
  8. J

    B Nuclear Fission & Creation of Plutonium

    Just joined the forum after youtubes algorithm suggested a story documenting the ‘Chicago Pile’. I ended up watching a bunch of other power plant videos becoming more confused with each one. I apologize up front as I know nothing about the field of nuclear physics and not even sure if I’ll even...
  9. CPW

    More info about natural nuclear fission going critical 2 Million years ago?

    This week I read through the chapter "Energy from the Nucleus" inside the familiar intro physics textbook Halliday, Resnick, Walker. I found it fascinating that there is evidence from a uranium mine in West Africa that there may likely have been a nuclear fission natural reactor that went...
  10. S

    How many neutrons are produced in nuclear fission?

    The nuclear fission reaction is: ##U_{92}^{235} + n^{1}_{0} \to Ba_{56}^{141} +Kr_{36}^{92} + 3 ~n^{1}_{0} ## I am not sure about the number of neutrons produced. Is it 2 or 3? 2 is from the number of neutrons on the RHS - number of neutron on LHS 3 is from the number of neutrons on RHS only...
  11. T

    Nuclear fission calculation of energy released

    Summary:: Calculate the amount of energy in joules generated from 2 kg of uranium fuel if the uranium 235 represents 0.7% of the metal and every fission releases 200 MeV. Hi! I am stuck in this question from my exercise book : Q. Calculate the amount of energy in joules generated from 2 kg...
  12. A

    Principle of Nuclear Fission Direct Energy Conversion

    Good day everyone, I've recently been researching direct energy conversion schemes for nuclear fission, and I have a question on the basic physics behind the device (specifically on how it converts kinetic energy to electricity). In essence, the "basic" scheme for fission DEC devices is that...
  13. Adams2020

    I The surface area of an oblate ellipsoid

    In "An Introduction to Nuclear Physics by W. N. Cottingham, D. A. Greenwood" for the surface area of an oblate ellipsoid, the following equation is written for small values of ε : The book has said this without proof. I found the following formula for the desired shape: No matter how hard I...
  14. B

    I Questions about the energy released by nuclear fission

    as far as i understand nuclear fission is the splitting of a heavy nucleus cause of a added neutron the energy you get is cause of the lost mass from binding energy. but i also read that the nuclear fission products undergo beta decay which emits beta particles gamma rays and antineutrinos so...
  15. Marasmusine

    HEU reactors vs. LEU reactors

    Summary:: How do high-enriched uranium reactors compare with low-enriched uranium reactors? Hello, I'm doing some research for a book, and there's some information about fission reactors I just can't find. I am comparing HEU fission reactors with LEU fission reactors ... even ballpark figures...
  16. Ranku

    I Exploring Natural Phenomena Similar to Nuclear Fission

    Is there any phenomenon in nature that resembles or is analogous to nuclear fission?
  17. C

    Safe zero base reactivity level nuclear fission reactor?

    There are already 4 generations of nuclear fission reactors. (Compare https://en.wikipedia.org/wiki/Nuclear_reactor#By_generation.) However among these, there does not seem to be a (maximum) safe nuclear fission reactor design, which immediately stops the nuclear chain reaction when the reactor...
  18. C

    B Energy conservation in nuclear fission

    Hi all, I struggle to understand how energy is conserved I fission. If the binding energy per nucleon increases, surely the mass defect simply accounts for that difference to conserve energy before and after. How does the mass defect account for the kinetic energy of the fission fragments as well?
  19. C

    I Why is Proton Radiation this Rare in Nuclear Fission Decay?

    The atomic nuclei consist out electrons, protons and neutrons (with only exception of hydrogen, that does have a neutron). Thus, it would be straightforward, that there existed a corresponding radiation for each nucleus component, when a nucleus decays. There is an electron radiation (beta...
  20. A

    B How energy is released during nuclear fission?

    In a simple nuclear fission reaction an uranium atom breaks into krypton and barium releasing around 200MeV. Binding energy per nucleon (BE/A) of uranium = 7.6 MeV And binding energy per nucleon of krypton an barium is just larger than that of uranium. So in my view, around 200 MeV is used to...
  21. V

    B Simple doubt in nuclear fission

    Hi all , I have a very simple doubt in the basics of radioactivity . Nuclear fission is the splitting of the nucleus of a heavy atom such as U23592 by bombarding with slow neutrons into two lighter nuclei with a simultaneous release of huge amount of energy . Now my doubt is that - Can a...
  22. DoobleD

    B Account for Coulomb repulsion in nuclear fission energy?

    Hi, I have learned that, in a nuclear fission or an alpha decay, the available energy released is the difference of masses between the initial nuclide (+ eventually some other initial particles) and the output particles, times c^2 (as E = mc^2). I'm fine with that. But I wonder : what about...
  23. Jam Smith

    B Nuclear Fission & Fusion: Explained for Newbies

    http://physics.stackexchange.com/questions/249809/why-only-light-nuclei-are-able-to-undergo-nuclear-fusion-not-heavy-nuclei Can anyone please explain me - what is similar between Nuclear fission & Nuclear fusion? Why are only light nuclei able to undergo nuclear fusion, not heavy nuclei? I am a...
  24. R

    I Is nuclear fission a quantum fluctuation

    Nuclei of unstable isotopes spontaneously fission in a way that is measured in half-life. So for a particular nucleus at a given time, it is a probability of some amount, thus is a QM fluctuation? Then what is going on in reactors which in effect modify the nucleus half life by introducing extra...
  25. O

    Question about nuclear fission

    I was watching an explanation (found here: youtu.be/yTkojROg-t8 ) on nuclear fission. In the video, he described the process of fission to happen one a random neutron smashes into a uranium nucleus. This causes the necleus to split into krpyton and barium, taking part of the nucleon and...
  26. D

    B Can Elements Die? Nuclear Fusion & Element Creation

    How could an element and all its atoms die? With nuclear fusion they combine atoms, so are they also making elements?...is it possible to make an element shooting the right number of p+,n, & e- and then contain it/save it for later?
  27. victorhugo

    B Is this how nuclear fission occurs with neutron bombardment?

    When neutrons are fired at atoms, if at higher speeds they will behave as waves, wander through and scatter, (which can produce something similar to x-ray diffraction images), but if slowed to the right "thermal energy" speed, they will be captured by (say) U-235, making the U atom unstable...
  28. J

    B Can someone walk me through nuclear fission?

    Its been a long time since I've studdied chemistry, I used to have a pretty decent understanding of it, but I've forgotten some of it. I remember that the energy produced from a fission reaction has to do with the number of bonds being broken, and that bonding energy released is obscenely high...
  29. A

    Struggling with Uranium-235 Nuclear Fission

    Homework Statement I've attached the question I'm having trouble with. Homework Equations The Attempt at a Solution I got an answer of 1.70375 * 10^-3 for the binding energy of a nucleus of uranium 235. For the third part, "When a uranium-235 nucleus undergoes fission..." I read the value of...
  30. R

    Can Nuclear Fission and Fusion Power a Bicycle?

    is it possible to create a bike involving nuclear fission and fusion . by using any nuclear reactant.
  31. S

    What is the Condition of Nuclear Fission?

    According to the experimental curve of Binding Energy per nucleon vs Mass no. , we have come to know that heavier nuclei having less B.E. are fissionable. We have also learned from Neutron vs Proton curve that those nuclei having N/P>1 can show radioactivity. But my question is why not all heavy...
  32. U

    Nuclear Decay - Semi Empirical Formula

    Homework Statement (a) What processes changes atomic number by 1? What are the favourable conditions? How do you tell a neutrino is involved? How can we use this to understand the mass of this particle? (b) Use semi empirical mass formula to explain why odd-odd isobars are unlikely, while...
  33. Saracen Rue

    I understanding this nuclear fission process

    Hi, I'm currently doing an assignment on nuclear physics. One of the questions in said assignment is asking me to state the decays which usually happen within a nuclear power plant, as well as stating the fission products, explaining what's happening, and showing the equation. One of the sites...
  34. O

    Nuclear Fission Equations and Fragments

    Homework Statement Our instructor asked to find 6 nuclear fission equations related to 235u. I found only 1-2 example. But none of them has shown the steps about fragments to be stable and thermal energy created in that equation. I know it was a mistake. Please help me out. Homework...
  35. U

    Simple expression for Coloumb energy

    How did they arrive at this expression? I understand the ##Q^2## term in the nominator and the ##r = r_0 (A)^{\frac{1}{3}}## term in the denominator. Where did the ##\frac{\alpha}{2}## term come from? Putting in Z=40, A=100 gives ##3.3 \times 10^{14} J##, not ##65 MeV##. The energy term...
  36. Evanish

    NASA An idea for a Pu-238 replacement for NASA space missions

    So I was reading this article about http://www.wired.com/2013/09/plutonium-238-problem/all/ and it got me thinking about possible substitutes. This is what I came up with. You make thin sheets of beryllium mixed with some kind of alpha particle emitter. You also make thin sheets of some...
  37. R

    Nuclear fission in an atomic bomb

    A person said: "However uranium-235 (U235) makes up only 0.72% of normal uranium metal and has to be separated from the remainder (mostlyuranium-238) in special factories which makes uranium-235 (U-235) a little more expensive. An uranium-235 (U-235) atomic has three neutrons less than an...
  38. K

    Nuclear fission and nuclear to thermal energy conversion

    Homework Statement [/B] Suppose the main water pipe breaks in a nuclear power plant, shutting off the water flow. If the control rods fall immediately into place, stopping the chain reaction, is there still a problem? Yes, because radioactivity continues to create lots of thermal energy. (A)...
  39. S

    Nuclear Fission Reactor Exam Question

    Homework Statement I have been able to complete all questions apart from part e) Homework Equations Beta minus decay involves electron emission Beta plus decay involves positron emission Electron capture takes in an electronThe Attempt at a Solution I believe that because there is an...
  40. majid313mirzae

    Vandenbosch, Huizenga. Nuclear Fission

    i want this book- can anyone help me? Vandenbosch, R. and J. R. Huizenga. Nuclear Fission, Academic, New York, 1973.
  41. N

    Controlling Nuclear Fission Geometry

    Hi everyone, I'm an engineer and not a physicist, so forgive me if something sounds stupid. Question: Is it possible to know, which way products of nuclear fission (u-235) will go? Imagine a sheet of single (or few) atom layer crystal of U-235, that is irradiated by neutron source from...
  42. sunrah

    Is the potential barrier of a nucleus related to its binding energy and size?

    I am confused about spontaneous fission. My basic understanding is that like α-decay the tunnel effect is responsible. We have a potential barrier caused by the superposition of surface tension energy and coulomb potential through which an energised nuclear fragment can tunnel with a certain...
  43. U

    Energy released in nuclear fission problem

    Homework Statement Homework Equations The Attempt at a Solution (a) Shown. (b) W = 975 MeV (c) Initially nucleus has volume V. Splits into two smaller particles each with charge Q/2, and volume V/2. So for each particle, Q/2 and R*(1/2)1/3 So, W' ~ 2 *...
  44. jaumzaum

    Energy dissipated by a nuclear fission

    In a nuclear fission of the uranium for example, the uranium atom can be subdivided in Kr and Ba + 2 neutrons + energy dissipated. This energy comes from the mass defect of the uranium in relation to Kr+Ba+2 neutrons. Is this energy full released in the form of photons? Is this energy full used...
  45. K

    Unpacking Nuclear Fission: Understanding Binding Energy

    During nuclear fission a heavy nucleus of low binding energy splits into two middle mass nuclei with high binding energy ! From where does this energy suddenly come from ?? And why is the binding energy of heavy nuclei lesser than that of middle mass nuclei ??
  46. D

    What is the Largest Nuclear Fission Model?

    For our last physics and chemistry project at Tully High, we broke the record for the Largest Nuclear Fission Model with mousetraps and ping pong balls! The record can be viewed via the following link
  47. K

    How much energy does the nuclear fission in one uranium atom give?

    Does it give a lot or is nuclear fission only powerful when you have a large quantity?
  48. T

    Conditions for nuclear fission

    Homework Statement not an equation as such. new to this but i wanted to know what the conditions for nuclear fission are? other than high temperatue and pressure Homework Equations "state the conditions for fusion and hence explain why it has proved difficult to maintain a sustainable...
  49. E

    Nuclear Fission and fissionable isotopes

    Hi, My textbook says that only Uranium and Plutonium are fissionable but it doesn't say why. Do smaller isotopes become bigger when they are bombarded by neutrons instead of spitting apart? Thanks
  50. B

    Why not use proton bombardment to trigger nuclear fission?

    Fission type nuclear bombs and nuclear reactors use neutron bombardment to trigger the fission reaction but why not protons? Protons can repel the like electromagnetic fields of the other protons in the atomic nucleus so why not bombard the nucleus with protons instead?